In the travelling-wire electroerosion machine, the continuous electrode wire is axially transported from a supply means to a takeup means. In the path of wire travel, a pair of machining guide members are commonly disposed at opposite sides of the workpiece to define a straight line path therebetween for the transported electrode wire. The latter is thus tightly stretched across the guide members while axially traveling continuously and traversing the workpiece and the guide members serve to position the electrode wire in a machining relationship with the workpiece. The machine further includes a power supply for passing an electrical machining current, typically in the form of a succession of pulses, between the electrode wire and the workpiece across a machining gap flooded with a machining liquid, e.g. water, to electroerosively remove process from the workpiece. As the material proceeds, the workpiece is displaced transversely relative to the axis of the electrode wire along a prescribed feed path under the command, preferably, of a numerical-control (NC) unit, so that a desired cut is formed in the workpiece.
A traveling-wire electroerosion machine is generally and commonly required to machine a number of cuts or contours in a workpiece or similar workpieces in a sequence of operations. In each operation, it is necessary that machining should start with a through-hole preformed at a given point associated with each contour desired. Thus, prior to proceeding with any given machining operation, the wire electrode must be threaded or set through a starting through-hole and, subsequent to accomplishment of such machining operation, the wire electrode must after removal from the machined contour or the hole be again threaded or reset through another preformed starting through-hole associated with another contour to be machined in the same or another workpiece. Each resetting operation needed after a given machining operation and before another therefore requires breaking, at a region immediately above or below the workpiece, the electrode wire extending continuously between the supply and takeup sides, re-aligning the relative position between the said axis of the electrode wire and the worktable carrying the workpiece or workpieces, threading a broken end portion of the electrode wire through the starting through-hole associated with the contour to be machined, and then reloading the threaded electrode wire in the wire axial drive or transportation means downstream of the downstream guide member to re-establish its continuous axial travel from the supply side to the collection side.
In order to eliminate the necessity for the operator's manual intervention, an automatic wire resetting arrangement has advantageously been provided which is designed to execute the foregoing wire resetting operation automatically. For such prior art, reference may be made to U.S. Pat. Nos. 3,891,819 and 3,987,270. With known setup arrangements, however, a difficulty on threading arises due to the extreme thinness (e.g. less than 0.5 mm thickness) of the electrode wire and the consequential poor self-supporting ability of the wire. As a matter of practice, thus, it has been found that very often an electrode wire is deflected prior to entry into a small starting through-hole or otherwise is caught on a wall portion of the through-hole and also even on a wall portion of a guide member for guidingly accepting the electrode wire.